1. Field of the Invention
The present invention relates to a silicon structure which can be applied to a light-emitting device or a solar battery, the method and apparatus for producing the same, and a solar battery using the silicon structure.
2. Disclosure of the Prior Art
In order to reduce the reflection of sunlight at its surface, a solar battery using silicon has been provided with an antireflection coating or an uneven surface.
The structure of a conventional solar battery will be explained with reference to FIG. 7, which is a cross-sectional diagram of a conventional silicon solar battery having a textured surface structure. As FIG. 7 illustrates, an uneven surface is formed at the light incident side of a p type silicon substrate 31 so as to reduce the reflection of the sunlight. Commonly used methods of forming the unevenness include a chemical formation method using photolithography and chemical etching, and a mechanical formation method using a dicing machine. Examples of silicon substrates include single crystal substrates produced by the Czochralski method and polycrystalline substrates produced by casting. An n type silicon layer 32 is formed on the uneven surface of the p type silicon substrate 31. The n type silicon layer 32 is formed by diffusing P (phosphorus) using a gas such as POCl3 on the uneven surface of the p type silicon substrate 31 so as to convert part of the p type silicon substrate 31 to n type. An antireflection coating 33 comprising materials such as SiN and MgF2 is formed on the n type silicon layer 32. Further, a front surface electrode 34 is formed on the light receiving side of the p type silicon substrate 31 via an n++ silicon layer 35, and the front surface electrode 34 is exposed on the surface of the antireflection coating 33. A back side electrode 36 is formed on the back side of the p type silicon substrate 31 via a p+ silicon layer 37. By forming a p+ silicon layer 37 between the back side electrode 36 and the p type silicon substrate 31, the energy conversion efficiency can be improved (see the Third xe2x80x9cHigh Efficiency Solar Batteryxe2x80x9d workshop preliminary reports, hosted by the Institute of Electrical Engineers, Semiconductor Electric Power Conversion Technology Committee, in Toyama, Japan, Oct. 5, 1992, Vol. A5-A6, pages 28-35).
Although the above mentioned conventional silicon solar battery configuration enables efficient collection of sunlight, the method of manufacture includes complicated processes to form the unevenness. This increases the production cost and thus the method is not suitable for practical use.
In order to solve the above mentioned problems in the conventional technology, an object of the present invention is to provide a silicon structure exhibiting little sunlight reflection, the method and apparatus for producing the same, and a solar battery using the silicon structure.
In order to achieve the above mentioned object, a configuration of the silicon structure of the present invention comprises an aggregate of a plurality of columnar silicon members mainly comprising silicon and having random orientations. According to the configuration of the silicon structure, since the light beam incident on one columnar silicon member is reflected thereby and re-enters another columnar silicon member, the sunlight can be absorbed efficiently. That is, according to the configuration of the silicon structure of the present invention, a silicon structure having little sunlight reflection can be obtained. It is preferable that the silicon content of the columnar silicon members is 95 weight % or more, and in addition to the silicon, about 1 weight % of chlorine and a few weight % of oxygen can be included.
In the above mentioned configuration of the silicon structure of the present invention, it is preferable that a substrate is provided and the silicon structure is formed on the substrate via a film mainly comprising silicon. According to the preferable embodiment, a transparent electrode does not come in contact with a lower electrode in the process of producing a solar battery using the silicon structure.
In the above mentioned configuration of the silicon structure of the present invention, it is more preferable that the diameter of the columnar silicon member is 0.1 to 10 xcexcm. According to this embodiment, an adequate strength of the columnar silicon can be maintained and the depth of the junction formed when converting to an n type or a p type does not need to be limited. Further, the light absorption does not deteriorate.
According to the configuration of the silicon structure of the present invention, it is further preferable that the periphery of the columnar silicon member is amorphous and the center thereof is polycrystalline.
Further, the silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon having random orientations can be produced by a method wherein an atomized or vaporized silicon material containing chlorine is introduced to a heated substrate with oxygen gas. According to this production method, since a silicon containing raw material less dangerous than silane gas (SiH4) can be used, the silicon containing raw material can be supplied in a great amount. As a consequence, since the silicon formation rate can be improved, a silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon can be obtained. In this case, an inert gas can be introduced to the substrate at the same time in order to convey a silicon containing raw material also containing chlorine. Besides, by conveying a silicon containing raw material with an inert gas including hydrogen, or with only hydrogen, the amount of chlorine in the silicon structure can be reduced. Further, since a complicated process to form an uneven shape is not necessary unlike with the conventional textured structure, the production cost can be reduced.
According to the production method of the silicon structure of the present invention, it is preferable that the silicon containing raw material also containing chlorine is Si2Cl6. According to the preferable embodiment, since the decomposition temperature is approximately 350xc2x0 C., which is low, and the decomposition can be conducted by radiating an ultraviolet beam (188 nm), a silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon and having random orientations can be obtained easily. In this case, it is more preferable that an n type or p type silicon structure is formed using a liquid material containing PCl3 or BCl3 as the silicon containing raw material comprising Si2Cl6.
In the above mentioned production method, it is more preferable that the oxygen gas is introduced so that the oxygen content in the vicinity of the centers of the columnar silicon members becomes 3% or less. According to this embodiment, the resistance of the silicon structure can be kept at a low level and thus the silicon structure can be used in an electronic device.
Further, an apparatus for producing the silicon structure of the present invention comprises a chamber, means to supply an atomized or vaporized liquid material comprising silicon and oxygen gas to the chamber, a support for the substrate to be treated by the apparatus, a heater for the substrate, and a filter having an area that is at least as large as the area of the substrate, through which the atomized or vaporized liquid material and oxygen gas are introduced to the substrate. According to the configuration of this apparatus, since the atomized or vaporized liquid material is uniformly diffused in the area of approximately the size of the filter at the time of passing through the filter and introduced to the surface of the substrate, a silicon layer can be formed uniformly on the substrate.
In the above mentioned production apparatus of the silicon structure of the present invention, it is preferable that the filter comprises a stainless steel fiber. According to this embodiment, a filter having a large area and a very large void ratio of from 70 to 90% and a uniform pore size can be formed at a low cost. And by dividing the vaporizing chamber and the process chamber with the filter, a pressure difference between the vaporizing chamber and the process chamber is unlikely to be generated and thus condensation of the material caused by adiabatic expansion can be prevented.
In the above mentioned production apparatus of the silicon structure of the present invention, it is more preferable that the pore size of the filter is 1 to 30 xcexcm. According to this embodiment, a raw material gas and oxygen gas can be sprayed on the substrate uniformly.
Further, a solar battery of the present invention comprises a semiconductor layer for generating electron-hole pairs by light absorption, wherein the semiconductor layer includes a silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon and having random orientations. According to the configuration of the solar battery, since the sunlight reflection is reduced, power generation can be efficiently conducted.
In the above mentioned configuration of the solar battery of the present invention, it is preferable that a substrate is provided and the silicon structure is formed on the substrate via a film mainly comprising silicon.
In the above mentioned configuration of the solar battery of the present invention, it is more preferable that the diameter of the columnar silicon member is 0.1 to 10 xcexcm.
In the above mentioned configuration of the solar battery of the present invention, it is further preferable that the periphery of the columnar silicon member is amorphous and the center portion is polycrystalline.
In the above mentioned configuration of the solar battery of the present invention, it is more preferable that the silicon structure is formed on the surface of the semiconductor layer at the side on which the light is incident.
In the above mentioned configuration of the solar battery of the present invention, it is further preferable that a pn junction is formed inside the columnar silicon. According to this embodiment, the following advantage can be achieved. That is, since the area of the pn junction portion can be increased in the case of a silicon structure comprising a plurality of columnar silicon members compared with the case of a conventional flat film, power generation can be conducted efficiently.